Scientific American’s Bering in Mind has a fantastic article on how the concept of the mid-life crisis was invented and whether it has any evidence behind it beyond the occasional inadvisable pair of cycling shorts and sudden interest in cheesy sports cars.
It turns out that the idea of the ‘mid-life crisis’ is surprisingly new – first touted in 1965 – but was invented to refer to a crisis of creativity in geniuses – rather than a sudden urge to dye one’s greying hair.
There isn’t actually any evidence that middle age is more of a time of crisis than any other period of life, but the concept has stuck.
In the decades since Jacques and Levinson posited their mostly psychoanalytic ideas of the midlife crisis, a number of more empirically minded psychologists have attempted to validate it with actual data. And with little success. Epidemiological studies reveal that midlife is no more or less likely to be associated with career disillusionment, divorce, anxiety, alcoholism, depression or suicide than any other life stage; in fact, the incidence rates of many of these problems peak at other periods of the lifespan.
Adolescence isn’t exactly a walk in the park either—as a teen, I’d worry so much about the uncertainties of my future that I vividly recall envying the elderly their age, since for them, no such uncertainties remained. Actually, old people—at least Swiss old people—aren’t fans of the “storm and stress” of adolescence, either. Freund and Ritter asked their elderly respondents which stage of their lives they’d prefer to return to, if they could. Most said middle age.
From another point of view, of course, the concept could also be a socially convenient way of helping to curtail certain behaviours in men when their actions are no longer thought to be age appropriate.
That’s my theory and I’m sticking to it.
Link to Bering in Mind on the mid-life not so crisis.
Mind Hacks 
Your theory appears reasonable. When you take into account that middle age is also when a man’s children are likely to have just left the nest there is usually some more disposable income for toys like fancy cars (kids are expensive). It’s a frustrating irony that when you’re young you often have to postpone the things you want in order to raise kids or save for retirement yet once you are able to do those things you are now too old for it to be “appropriate”.
like your explanation
I agree with you. If someone comes to the recognition that enjoyment is actually important in life; that you don’t have to live in a way that maximizes the ‘number of neighbors’ who approve of your choices; that the here-and-now should be relished … crisis? Hmmm. It sounds like an awakening. If it happens in mid-life, then a mid-life awakening. Although it may be a crisis for those around you.
Dante Alighieri, The Divine Comedy, written between 1308 and 1321:
Midway in the journey of our life
I came to myself in a dark wood,
for the straight way was lost.
Ah, how hard it is to tell
the nature of that wood, savage, dense and harsh -the very thought of it renews my fear!
It is so bitter death is hardly more so.
Looks like a poetic description to me.
A Convenient way of curtailing certain behaviors in men…is quite specific to the definition and there-in lies the question – do women have mid life crisis concerns as well – share